1. Field of the Invention
The present invention relates to a flame-retardant flexible polymer composition used as a material for forming polymer tubes, in particular, to a flame-retardant flexible polymer composition used as a material for forming heat-shrinkable tubes used for rendering, waterproof and insulated, electric wires and wiring harnesses and portions thereof where wires are bound together. The present invention also relates to a polymer tube formed from the flame-retardant flexible polymer composition and an insulated wire including an insulation formed from the flame-retardant flexible polymer composition.
2. Description of the Related Art
In order to render, waterproof and insulated, electric wires and wiring harnesses used for automobiles, aircraft, and the like and portions of the electric wires and wiring harnesses where wires are bound together, heat-shrinkable tubes are used that are tubes formed from chlorinated polyethylene, polyvinyl chloride, or the like and having heat-shrinkability. There is sometimes a demand for heat-shrinkable tubes having high performance in terms of oil resistance, heat resistance, flame retardancy, and mechanical strength, for example. In order to meet this demand, various polymer tubes have been proposed. Various polymer compositions serving as materials for forming these tubes have also been proposed.
For example, Japanese Unexamined Patent Application Publication No. 2011-225673 discloses a polymer tube formed from a wear-resistant polymer composition containing, as main components, 50 to 100 parts by mass of a chlorinated polyethylene, 50 to 0 parts by mass of a high-density polyethylene, and, relative to 100 parts by mass of the total mass of the chlorinated polyethylene and the high-density polyethylene, 1 to 10 parts by mass of hydrotalcite; the polymer tube being formed by irradiating the polymer composition with radiation to cause cross-linking. This publication states that this wear-resistant polymer composition is applied so as to cover a conductor to thereby provide an insulated wire including an insulation that is excellent in terms of wear resistance as well as flexibility, heat resistance, oil resistance, flame retardancy, and processability.
Japanese Unexamined Patent Application Publication No. 2013-018935 discloses a flame-retardant flexible polymer composition including a polymer component containing a chlorinated polyethylene as a main component and, relative to 100 parts by mass of the chlorinated polyethylene, 0.5 to 20 parts by mass of a zeolite compound; and a polymer tube and an insulated wire including an insulation, the polymer tube and the insulation being formed from the flame-retardant flexible polymer composition through cross-linking caused by irradiation with ionizing radiation. This publication states that this polymer tube is excellent and highly balanced in terms of mechanical strength, flexibility, heat resistance, oil resistance, flame retardancy, and processability.